Traditional methods used for filling ordnance with polymer bonded explosive (PBX) utilize a filling process based on the combination of usually two materials, namely an explosive mixture (pre-mix) and hardener, which are mixed together immediately prior to use in filling the chosen ordnance.
In a typical application of the mixing and filling process, a pre-mix of explosive such as, for example, PBX is produced and typically mixed with a hardener (i.e., IPDI), the combined mixture being mixed together in a high shear mixer.
Once mixed, the bowl of the high shear mixer containing the fully mixed PBX composition is fitted with a pressure plate apparatus and cover, then raised to an appropriate filling height on a specialized bowl lift.
Once elevated into position, the bowl of fully mixed PBX composition is pressurized using an inert gas (i.e., nitrogen) for the purposes of aiding the dispensing of the fully mixed PBX composition through a system of pipes to the ordnance filling position.
Ordnance to be filled is typically placed in a vacuum chamber and a filling attachment from the bottom outlet valve of the mixer bowl containing the fully mixed PBX composition is attached to the chamber. Typically, the vacuum will be evacuated to <100 millibars.
The vacuum provides the physical motivation for the fully mixed PBX composition to flow into the ordnance when the valve from the bottom outlet of the mixer bowl is released. The quantity of fully mixed PBX composition introduced to the cavity within the ordnance is usually judged visually, and when sufficiently filled, the vacuum to the chamber is released and the filled component removed ready for the introduction of the next ordnance component to be filled.
The traditional method of filling ordnance as described above suffers from a number of problems associated with the finite ‘pot life’ time of the fully mixed PBX composition and the fact that once the various chemicals have been combined, the ‘pot life’ time defines the period within which the filling process must be completed before the PBX composition cures and can no longer be used in the process (i.e., would solidify within the pipe work).
The ‘pot life’ is typically in the order of two hours and in instances where there are no problems associated with a particular batch of components, then the mixing of PBX and hardener (IPDI) in a bowl and the subsequent dispensing of the fully mixed PBX composition into ordnance can be achieved relatively quickly. However, if for any reason (for example, mechanical breakdown, etc.) the filling process has to be interrupted or indeed suspended, then the whole of the fully mixed PBX composition has to be purged from the mixing and filling apparatus, the purged material being lost to waste.